Experimental Apparatus

The apparatus you will use for this experiment is shown in Figure 1. A metal fiber is strung vertically through the center of the apparatus, with a copper disk, shown in Figure 2, mounted in the middle. Strings are tied around the rotor shaft and attached to pulley’s on either side of the apparatus, allowing students to use the gravitational force on known masses as the applied torque on the rotor. Markings on the copper disk allow students to easily determine the number of radians that the wire twists through.

Figure 2: The copper disk in the torsional oscillator apparatus

For the copper disk used in this experiment, the manual says that the mass is 962(2) g, inner diameter is and the outer diameter is (sorry for imperial units; the apparatus was made in America).

The apparatus includes an electrical position transducer located below the copper disk. The details of how this position transducer works are not super relevant to your experiment. Just note that it does not rely on having physical contact with the rotating system, so it does not impede the rotational motion, and that it has a response time of about 10 ms, which is far faster than the rotational period of the system.

The apparatus includes a set of brass quadrants that students can use to measure their rotational inertia in various arrangements, and compare to theoretical calculations. Four of these quadrants together make an arc with an inner diameter of 1.72” and outer diameter of 3.72”. Each quadrant has a mass of 214.5(5) g.